Continuation of the limb twist experiment.

[gfugal]

So for some reason, my thick-headedness or whatever, I wasn't grasping the limb twisting concept. So I settled to do the same experiment 4est Trekker did. I wanted to actually see what happened as I unbalanced the string alignment myself. I particularly was interested in what the back of the bow would do. I wanted to know if the strong side or the weak side raised up. I also wanted to provide before and after pictures for others, because I wasn't sure how much twist was due to the levelness of the back or the surface or maybe how it was clamped. Lastly, I also thought it would be an added bonus to see how the tiller for uniform thickness would look.

[gfugal]

First I'll show the tiller from uniform thickness. It was a simple piece of red oak timber I got from Lows. I reduced its width a little bit, put knocks in it, then strung it up. I braced it to six inches as shown in the first picture


then drew it to 19 inches


It is 48 inches in length TTT. It wasn't very strong only about 7 lbs at the 19 inches, but I did get it to 22 inches which surprised me that it worked so easily and could bend that far without breaking despite no tillering or adjustments at all. As you can see the handle area is over-bending and the tips are stiff. This was to be expected but it's good to actually see it.

[gfugal]

Next, I'll show pictures before and after the uneven wood removal. I didn't have a square, so I just used a level. You can see if you look closely that the table top is level so when it's standing up perpendicular like that it should be square.

This picture is of it un-altered from the front view


And this is the same one un-altered from the opposite side. I just turned the table around to keep the background the same.


Those previous pictures were before I altered it, and these next two are after I altered it. I apologize that the two altered pictures seem to show the twist going one way in one picture than the other way in the next. I wanted to keep the same background view, so to get the picture of the twist from the opposite side, I just turned the table around instead of walking over there. I assure you it does throw off the alignment and pulls toward the weak side in both the cases of those last two photos,  just like 4est Trekker previously discovered.

This is the altered from the front. The weak side is to the left in this picture


This is the altered from the back. The weak side is to the right this time due to turning the table around.


What I did was taper the limb by removing wood from only one side (refer to the next post for more explanation). What was surprising to me was how I couldn't really tell the alignment was off until I clamped it flat to the table. I could tell something was off, and because I was purposefully altering it I knew it was the alignment, but if I didn't know any better and this was happening on a real bow I might not have noticed this was happening, not unless I was watching carefully.

[gfugal]

To show how I took off the wood to throw off the alignment, refer to these two pictures. For convenience, and because most bows have a stiff handle, I left the handle and tips unaltered. I was also curious if that would affect it in any way. After taking the pictures I shaved off the extra wood on the handle and tips and re-strung it. It didn't seem to change anything so I didn't bother to photograph it again. It seems the alignment issue results mainly from the working sections of the limbs, with little effect from the tips or handle.

[gfugal]

Finally, I not only wanted to see the effects the uneven tiller had on string alignment but I wanted to identify other signs too, like back and belly elevation.
 
In this picture, you can see how far off the alignment is. It pulled it off maybe an inch or so from the center. This made it where it no longer went over the bow.


This picture shows the other sign--the twist of the limb. If you look at the tip you see that they are twisted. The strong side twists up, and the weak side lowers down (if you're looking at the back string down).


This image zooms in on the back and shows that you can see this elsewhere besides just the tips. The back is raised ever so slightly on the left side if you look closely. 


If you were to flip it and look at the belly the opposite would be true. The weak side would rise up and the strong side would be lower. So if you're tillering and you see that one side is higher than the other, it may be tempting to file that down but STOP. Don't and re-evaluate. if a side is raising on the belly that probably means it's weak. Instead, you should take from the lower side.

This last image is the back before it was altered. If you zoom in you can see that it isn't raised like it is in the others. (sorry, my finger is in the way of the tip, but I assure you it is level with no twist).

[gfugal]

I hope this better solidifies the concept for some of you. I know I couldn't wrap my head around it and just found myself staring at the pictures by 4est Trekker. I just was wishing there were more pictures. So that's what I did. I made more of them.  If it still doesn't click then maybe you'll just have to do it yourself too. 

[Del the cat]

I appreciate you taking the time to do this it is surprisingly difficult to get good clear pics and explanation.
An experiment and some pics is always good.
Just a little point... there is a typo' in the post where you say first two picture before and second two "before" when presumably you mean "after".
Maybe you could clarify ('cos it doesn't show in the pic) The edge with the wood removed (weak edge) is the edge along the side of the table? Yes?
Thanks again for posting.
Del

[gfugal]

Thanks for pointing that out. I altered the original post. Hopefully it makes more sense now.

[Jim Davis]

It would have been much more clear with just captions for each image. As is, the mind spins around like the table.

[gfugal]

I didn't know there was a way to do that. But now I see there is an insert image option. Let me try and fix it.

[gfugal]

Well, I tried to fix it but it wasn't letting me modify it, for now, I guess just look at the picture name which is very small underneath it. Maybe that will help. How do you guys insert pictures with captions and stuff? Or how do you do it from other sites like Imgur and Photobucket?

[gfugal]

Ok, I edited the post. The pictures are in the text now, most with captions. Hopefully, that clears things up some more. Again I apologize, this post was testing my formatting skills. I should be done with all the modifications now unless there is another issue.

[George Tsoukalas]

The bow twists towards the weak side. The weaker side is the one closest to the string in the braced bow. Strong side is furthest.

Fix: remove wood from the strong side in small increments and draw the bow at partial draw for changes to register.

I only fix it if I caused it. Some staves are naturally twisted. If the twists is minimal, I leave it.

Caveat: just because your measurements show even wood removal doesn't mean
that is sufficient for the bow.

I once painstakingly removed wood from a yew stave all the while checking with calipers to insure even wood removal.

When I strung the stave she was a leaner(twisted on the same side on upper and lower limbs) and I had to fix as I have described above.

Jawge

[gfugal]

Yes just cause a limb has uniform thickness doesn't mean it won't have twist when strung. In those cases it probably has to do with some property of the wood, maybe it's denser on one side, maybe the grain is doing something funny, or maybe there are knots or imperfections on the other. I was actually surprised how good the string alignment was on this scrap piece without any adjustment. If you look at the end grain it's not even parallel with the back but the board was sawn at an angle. What the experiment did show if you start off with good alignment you can for sure foul it up by uneven wood removal.

I would agree that it's much harder to try and fix string alignment if that was due to misaligned tips or natural twist. I don't know if removing wood from one side would do enough to fix that, without causing other problems. It might be better to heat treat in that situation or just deal with it. Good distinction.

The bow twists towards the weak side. The weaker side is the one closest to the string in the braced bow. Strong side is furthest.

That's another good way of saying the belly rises up on the weak side (raises closer to the string), and the strong side lowers (moves further from the string). However, if the limb has natural twist using this method may not work as easily as you point out, because you don't know if it's raising due to being weak, or raising because that's how it's naturally twisted.

[willie]

Greg

interesting experiment. I can see two pics in Reply #3, and no other pics in the rest of the thread. Are there more?